Composite structures such as those used in the automotive, marine and aerospace industries may be fabricated using automated composite material application machines, commonly referred to as automated fiber placement (AFP) machines. AFP machines may be used in the aircraft industry, for example to fabricate structural shapes and skin assemblies by wrapping relatively narrow strips of composite, slit fiber tape or “tows” around a manufacturing tool. The AFP machine aligns and places a plurality of the tape strips, typically six or more, in continuous, edge-to-edge contact forming a single wide, conformal bandwidth which is placed on and compacted against the tool.
In the past, AFP machines have been relatively large and complex in order to provide features and functions that allow them to fabricate a wide range of large scale structures. During tape placement, the fiber tape is drawn from spools of the tape mounted on the machine. It is necessary to maintain a proper amount of tension on the fiber tape as it is drawn from the spools, and to compensate for slack in the tape which may occur during normal AFP machine operation. Tensioning of the fiber tape is controlled by a relatively complicated feedback system that employs a looped network of servo motor drives and sensor arrays. Other tensioning systems have employed a rotational drag brake and release mechanism combined with external torsion spring biased rollers to compensate for variations in tape slack.
More recently, smaller, simplified AFP machines have been proposed that are capable of placing narrower fiber tows, and are therefore may be better suited for fabricating smaller structures and components. Although the mechanisms used in the fiber placement heads of these simplified AFP machines are smaller and have reduced complexity, the machines nevertheless utilize standard size spools of composite fiber tape of the type discussed above. The use of known, relatively complicated fiber tensioning systems may not be compatible with these smaller AFP machines.
Accordingly, there is a need for a simplified fiber tensioning device that may be used with simplified AFP machines using standard size spools of tape.